This invention relates to chelated transition metal catalyst component in the presence of magnesium halide, a process for olefin polymerization using said catalyst component, and, more particularly, novel olefin polymerization catalyst containing transition metal compound chelated by chelate ligand which can copolymerize ethylene and xcex1-olefin and produce a polymer having a narrow molecular weight distribution and compositional distribution.
Metallocene compounds are known to be an excellent catalyst for (co)polymerization of olefin and have been improved through the modification of cyclopentadienyl ligand to indenyl ligand, fluorenyl ligand, or bridged ligand. Also, there have been developments of supported metallocene catalytic system producing polyolefin with excellent morphology, which can be applied to slurry process or gas phase polymerization process. For example, in U.S. Pat. Nos. 5,439,995 or 5,455,316, they reported that the supported titanium metallocene or zirconium metallocene catalytic system showed excellent copolymerization and morphology properties. However, they still have some disadvantages such as synthetic difficulties, modification of existing polymerization process, and poor processibility of the produced polymer due to its narrow molecular weight distribution. Also, the activating components for metallocene catalysts such as MAO(methylaluminoxane) compounds or boron compounds are still quite expensive to be applied for polyolefin materials with general purpose.
Recently, they have been employing oxygen or heteroatom bound chelated transition metal compound as homogeneous catalysts for olefin polymerization, which are called non-metallocene catalysts or organometallic catalysts, and it attracted much attention, because these compounds are easier to synthesize than metallocene compounds and are known to show equivalent properties to metallocene compounds. Similar to the metallocene catalysts, these catalysts are anticipated to display excellent (co)polymerization ability, and there have been active investigation of oxygen or heteroatom bound chelated transition metal compounds as a catalyst component.
Japanese Laid-Open Patent sho 63-191811 disclosed the chelated catalysts for ethylene and propylene polymerization where chlorides of titanium chloride compound are replaced by TBP ligand(6-tert-butyl-4-methylphenoxy), and methylaluminoxane(MAO) is used as a cocatalyst. It was reported that polymerization of ethylene and propylene yielded polymer with excellent activity and high molecular weight(Mw=3,600,000). U.S. Pat. No. 5,134,104 reported chelate catalysts employing amine ligand substituted halide titanium compound, {(C8H17)2NTiCl3}, and the results of olefin polymerization with these catalysts. And in J. Am. Chem. Soc., 117, 3008, catalysts using oxygen bound chelated transition metal compounds which localize the coordination sphere of transition metal compounds were introduced. Also, transition metal compounds chelated with phenoxy derivative ligands were reported in Japanese Laid-Open Patent hei 6-340711 and EP 0606125A2, which produce high molecular weight polymer having narrow molecular weight distribution with MAO as cocatalyst.
However, the investigated organometallic catalyst or non-metallocene catalysts have never reported examples of copolymerization of xcex1-olefin, and they have never been used as a heterogeneous catalyst for olefin polymerization, which can control the morphology of polymer. Also, they have never reported examples of polymer having broad molecular weight distribution, which shows good processibility. On the other hand, conventional TiCl4 based Ziegler-Natta catalyst, being heterogeneous catalyst, can produce a polymer having good morphology, good processibility, and broad molecular weight distribution. However, when low to medium density polyethylene is desired to obtain using conventional TiCl4 based Ziegler-Natta catalyst, compositional distribution of the resulting copolymer tends to be very broad. Furthermore, high quality copolymers capable of being formed into films having excellent transparency, antiblocking property and heat sealing property are difficult to be obtained.
Therefore, the catalyst having hybrid character between conventional Ziegler-Natta catalyst and single site catalyst, which can produce the copolymer having narrow compositional distribution and good morphology and processibility, has been desired.
The objective of this invention is to provide the catalytic system for olefin polymerization employing chelated transition metal compound containing chelate ligand in the presence of MgCl2 material having a spherical shape as support, which are capable of giving ethylene/xcex1 olefin copolymer having narrow molecular weight distribution, narrow compositional distribution, excellent morphology, and good processibility.
According to this invention, the olefin polymerization catalytic system comprises chelated transition metal catalyst component[A], MgCl2 support component[C], and aluminum cocatalyst component[B].
The preparation of chelated transition metal catalyst component[A] are prepared by the unique synthetic method, in which Mg[AlRxe2x80x2(OR)3]2 reacts with chelate ligand to form Mgxe2x80x94Al-chelate ligand complex containing chelate ligand, and this complex reacts with metal halide compound to prepare chelated transition metal compound which is quite soluble in non-polar solvents.
Aluminum cocatalyst component[B], to activate the catalyst component[A], employs general organoaluminum compounds of formular R3Al or R2AlCl (R=hydrocarbon). And the catalytic system of this invention does not have to use expensive MAO(methyl aluminoxane) or boron compounds are cocatalyst.
MgCl2 support component[C] is solid MgCl2 having a spherical shape which can be prepared from the known method or MgCl2 on the surface of silica which is available from the supplier.
The catalytic system of this invention may be used to produce ethylene copolymer from ethylene and at least one alpha-olefin having 3 or more carbon atoms in which the copolymer has narrow molecular weight distribution, narrow comonomer compositional distribution, excellent morphology, and good processibility.
These and other features, aspects, and advantages of this invention will become better understood with reference to the following description and appended claims.
In this invention, the term xe2x80x9cpolymerizationxe2x80x9d used herein is intended sometimes to include not only homopolymerization but also copolymerization, and the term xe2x80x9cpolymerxe2x80x9d used herein is intended sometimes to include not only homopolymer but also copolymer.
According to this invention, the chelated transition metal catalyst component[A] is prepared by the reaction of Mg[AlRxe2x80x2(OR)3]2 with chelate ligand to form Mgxe2x80x94Al-chelate ligand complex [M-2] containing chelate ligand as described in equation (1-1)
Mg[AlRxe2x80x2(OR)3]2+chelate ligandxe2x86x92Mgxe2x80x94Al-chelate ligand complex[M-2]
Mgxe2x80x94Al-chelate ligand complex[M-2]+MX4xe2x86x92Transition metal component[A]
where R and Rxe2x80x2 are independently alkyl or aryl group; M is Ti or Zr; X is halogen atom.
Mg[AlRxe2x80x2(OR)3]2 can be prepared through the reaction of Rxe2x80x22Mg with Al(OR)3. Al(OR)3 is simply prepared by adding ROH to AlRxe2x80x33, where R, Rxe2x80x2 and Rxe2x80x3 are independently alkyl or aryl group. The reaction of AlRxe2x80x33 with ROH produces exothermic heat and liberate Rxe2x80x3H. The exothermic heat and liberation speed of Rxe2x80x3H can be controlled through the slow addition of ROH to AlRxe2x80x33. The mole ratio of AlRxe2x80x33 to ROH is preferred to be 1:3. The reaction of Al(OR)3 with Rxe2x80x22Mg produces mild heat of 5xc2x0 C., and the reaction goes smoothly at the room temperature. The mole ratio of Al(OR)3 to Rxe2x80x22Mg is preferred to be 1:2, and the reaction is completed by stirring the mixture of two components for 3 to 5 hours.
Mgxe2x80x94Al-chelate ligand complex[M-2] containing chelate ligand can be obtained by the reaction of Mg[AlRxe2x80x2(OR)3]2 with chelate ligand with mole ratio of between 1:1 and 1:2. Depending on the type of chelate ligand, the reaction could produce mild heat. However due to the Al(OR)3 complexation, the exothermic heat is usually not produced, and the reaction could be done at the room temperature. Depending on the ligand type, the reaction time could be changed, but generally the reaction needs to be done for at least 6 hours to complete at the room temperature. Regarding chelate ligand compounds, various types of chelate ligands can be employed for the purpose of this invention. For example, carbodiimide type compounds such as dimethylcarbodiimide, dicyclohexylcarbodiimide, 1,3-bis-trimethylsilylcarbodiimide and the like; or diketiminato type compounds such as 2-(p-tolylamino)-4-(p-tolylimino)-2-pentene, 2-((2,6-diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene and the like may be used. The preparation method for diketiminato type ligands are reported in Organometallics 1998, 17, 3070 and Tetrahedron Letter 1990, 31, 6005.
Transition metal catalyst component [A] containing chelate ligand can be prepared through the methathesis reaction of Mgxe2x80x94Al-chelate ligand complex[M-2] with metal halide compound such as TiCl4, TiBr4, TiCl2(OR)2, TiCl3(OR), TiBr2(OR)2, and TiBr3(OR) (where, R is alkyl or aryl group) at the room temperature. To help the separation of MgCl2 or to cause a smoother reaction, it is preferred to use Lewis base adduct of metal halide such as TiCl4(THF)2. The reaction needs at least 12 hours to complete at the room temperature, and the separation of MgCl2 can be done easily through the filtration since MgCl2 is not soluble at all in hydrocarbon solvents. As a medium for reaction, non-polar solvents such as aliphatic or aromatic hydrocarbon solvents are preferred.
One of the specific feature of this invention is that the preparation method of chelated transition metal catalyst component does not include any complicated separation procedure or any heating so that the industrial scale preparation of this chelated transition metal catalyst component can be done simply without complication. Also, instead of using lithium salt or potassium salt compounds in the methathesis reaction to attach the chelating amide ligand to a metal, the incorporation of the unique Mg[AlRxe2x80x2(OR)3]2 compound which is soluble in non-polar solvents such as aliphatic or aromatic hydrocarbon makes the preparation much simpler and easier to do, since it does not include any polar solvents such as ether or THF to complete the methathesis reaction which is usually done in polar solvents. After the separation of MgCl2 from the reaction medium, the chelated transition metal catalyst component[A] solution in non-polar solvent medium is used without further purification or separation, since usually the specific incorporation of Mg[AlRxe2x80x2(OR)3]2 compound does make the chelated transition metal catalyst component[A] readily soluble in non-polar solvents such as aliphatic or aromatic hydrocarbon.
The MgCl2 support component[C] having excellent morphology may be prepared through the various known methods such as recrystallization of MgCl2 from electron donating solvents and the reaction of Grignard reagent with alkyl halides. Alternatively, silica containing 3xcx9c5% MgCl2 which is available from the supplier such as Grace Co. may be used.
The unique solubility of chelated transition metal catalyst component[A] in non-polar solvent enables a unique polymerization process, in which chelated transition metal catalyst component[A] in non-polar solvent, not being supported on MgCl2 support component[C], is directly put into the polymerization reactor in the presence of the separate MgCl2 support component[C] in the form of solid and cocatalyst component[B] to polymerize ethylene or ethylene/alpha-olefin. That is, chelated transition metal catalyst component[A] is not necessarily supported on the MgCl2 support component[C] to act as a catalyst. With separate injection of MgCl2 support component[C] and chelated transition metal catalyst component[A] into the reactor, the excellent morphology of polymer can be obtained in the slurry process. Also regarding the gas phase polymerization, through the prepolymerization as explained in the examples, the dry form of prepolymerized catalyst can be prepared to be injected to gas phase process to get polymer with excellent morphology.
Also, the immobilization procedure may be done by simply stirring the slurry mixture of the chelated transition metal catalyst component[A] in non-polar solvent and MgCl2 support component[C] at mild temperature such as 40 to 50xc2x0 C. The temperature of 50xc2x0 C. is preferred. The ratio of the chelated transition metal catalyst component[A] to the MgCl2 support component[C] is preferred to be 0.3 to 1 mmol per gram of MgCl2 support component[C]. After stirring the slurry mixture for about 3 hours, the supernant liquid portion is decanted and washed with hexane or heptane five times to get chelated transition metal catalyst component[A] supported on the inorganic support.
Ethylene (co)polymerization may be done using the catalytic system of this invention, which can employ either the catalyst component[A] in the form of solution with the separate MgCl2 support component[C] or the catalyst component[A] in the form of solid supported on the surface of MgCl2 support component[C], with organoaluminum compound as a cocatalyst component[B].
The catalyst component[A] can produce polymers having narrow molecular weight distribution(M.W.D.) or narrow compositional distribution. Therefore, the organoaluminum compound as a cocatalyst component[B] is not necessarily MAO(methylaluminoxane), modified MAO products or boron compounds to produce copolymers having narrow M.W.D. or narrow compositional distribution. With conventional organoaluminum compounds of the formular AlRnCl3xe2x88x92n, where R=alkyl group and n=2 or 3, as a cocatalyst component[B] such as TEA(triethylaluminum), TIBA(triisobutylaluminum), TMA(trimethylaluminum), TOA(trioctylaluminum), diethylaluminumchloride, and diethylaluminumsesquichloride.
With the catalyst component[A] in the presence of MgCl2 support component[C] and organoaluminum cocatalyst component[B] described in the above, ethylene can be copolymerized with an alpha-olefin having 3 to 10 carbon atoms, preferably 4 to 8 carbon atoms. Examples of the alpha-olefin having 4 to 8 carbon atoms include 1-butene, 1-pentene, 1-hexene, and 4-methyl-1-pentene.
In the polymerization process of this invention, the copolymerization of ethylene with alpha-olefin can be carried out in the liquid or gas phase in the presence of or absence of inert polymerization solvents such as hexane, octane, and cyclohexane. The amount of the chelated transition metal catalyst component[A], being supported or separated, can be varied. Measured per liter in the polymerization reaction zone, the chelated transition metal catalyst component[A] is used in an amount of preferably about 0.001 to about 0.5 millimoles per liter, calculated as transition metal atom. The ratio of chelated transition metal catalyst component[A] to MgCl2 support component[C] can be varied from 1.0 mmol/g-MgCl2 to 0.3 mmol/g-MgCl2. The organoaluminum cocatalyst component[B] is used in such an amount that the aluminum to transition metal atomic ratio is approximately from 5 to 100. The polymerization temperature may be approximately 40xc2x0 C. to 100xc2x0 C., and (co)polymerization may be performed in the presence of hydrogen to control the molecular weight of (co)polymer.
In this invention, the ethylene copolymer having a density of 0.910 to 0.945 g/cmxe2x80x2 can be produced without causing any problems such as the formation of substantial amount of ethylene copolymers soluble in hydrocarbon solvents and consequently the increase of viscosity of the copolymer solution causing reduction in stirring efficiency, blockage of pipes, and low efficiency of separating the copolymer from the reaction solvent. Also, the catalyst component[A] according to this invention can polymerize ethylene copolymer, having a density of 0.910 to 0.945 g/cmxe2x80x2 in gas phase process, without any reactor fouling through direct catalyst feeding to gas phase reactor or through prepolymerization, of which prepolymerized catalyst is fed to gas phase reactor. Specially, the catalytic system of this invention is suitable to polymerize ethylene copolymer having density of 0.910 to 0.945 g/cmxe2x80x2 with narrow molecular weight distribution and comonomer compositional distribution, and in turn, the ethylene copolymer can be used to produce a film having high impact strength property. Also, by using MgCl2 support component[C] having a spherical shape, either the catalyst component[A] being supported or separated, the catalytic system of this invention provides excellent morphology of polymer having bulk density of 0.40xcx9c0.45 g/cmxe2x80x2 and a spherical shape.